Women — especially moms — are underrepresented in top corporate and government jobs. But is what looks like inequality actually a savvy choice by women themselves?

That's the claim Fortune's Patricia Sellers made in a blog post yesterday. She was responding to David Leonhardt's Times piece about Sonia Sotomayor, Elena Kagan, and Harriet Miers — all female Supreme Court nominees, all childless. Leonhardt writes that while childless women make almost as much as men, moms are way behind in income and career advancement, because of "the harsh price most workers pay for pursuing anything other than the old-fashioned career path." But Sellers thinks any disparity has less to do with employer discrimination and more to do with employee choice. We've all heard variants on this argument before (women just want to make less money, because they hate work and love babies!) but Sellers has a slightly different take:

Women who could be Fortune 500 CEOs someday often don't chase the dream because they know there are better ways to fulfill a career. Particularly these days. In Gallup's 2010 Confidence in Institutions poll of 1,020 adults, "big business" ranks near the bottom, at 19% alongside HMOs. Just one institution rated lower: Congress, at 16%.

Small business comes in at the top, right behind the military (No. 1 again). Indeed, entrepreneurship lures a lot of women from the Fortune 500, at a higher rate than it attracts men.

Sellers isn't saying that women choose mommy tracks because they're lazy or soft or ill-suited to real work (though a source she quotes does call them "risk-averse"). She's saying they've realized that Fortune 500 boardrooms can be intolerant, inflexible places, and they've adjusted accordingly. It's an interesting argument — Leonhardt says "the best hope for making progress against today's gender inequality probably involves some combination of legal and cultural changes," and maybe women who start their own businesses can help change America's corporate culture. There's something kind of hopeful about the idea that women, instead of struggling against the rigidity of the Fortune 500 (a rigidity no longer even accompanied by job security), are striking out on their own.

Except that men still dominate the venture capital world, and male-owned companies get the lion's share of money from individual "angel" investors. And if we're talking about women in Congress and on the Supreme Court, change from the outside doesn't make as much sense — what, are women going to start their own legal system? Sellers is right that women's individual choices can be powerful — and if they're fleeing the Fortune 500, it might be a sign that the "old-fashioned career path" isn't working particularly well for anybody anymore. But we can't necessarily trust the Fortune 500 to listen, and it'll take more than a few female entrepreneurs to change workplace culture in America. It'll take everyone — men and women, employees and employers — recognizing that it needs to change, and lawmakers helping put that change into practice with (as Leonhardt mentions) better parental leave and childcare policies. Which is just one reason we need more women in government and in boardrooms — and why Sotomayor and Kagan can't remain anomalies.